The present invention relates generally to digital imaging systems. In particular, the present invention is a developer solution replenishment control system for use in conjunction with digital imaging and film processing equipment.
Media processors are commonly used in the medical field to develop media imaged by continuous tone digital imagers. Digital imagers of this type are configured to receive input data generated by a magnetic resonance (MR), computed tomography (CT) or other type of scanner. The input data is typically a sequence of digital values representative of the scanned image. Image processing electronics within the imager processes the input data to generate a sequence of digital exposure values, each of which is representative of one of a plurality of intensity levels (eg., a grey scale) at a discrete pixel location on the visually observable image. The image processing electronics scales and maps the range of scanned input data values to a range of exposure values which will produce a useful continuous tone photographic image. This mapping operation is necessitated by the nonlinear relationship between the input data and its visual representation, and the nonlinear sensitometric response of the photographic medium to different intensities of light. The image processing electronics typically includes a lookup table of stored data characterizing the input data to exposure value transfer function. The lookup table is accessed by the image processing electronics as a function of the input data to determine associated exposure values.
The imager uses the exposure values to modulate the intensity of a laser or other beam of radiation as the beam is scanned about a photosensitive medium. The intensity of the radiation beam, and therefore the degree to which the photosensitive medium is activated at each pixel location, corresponds to the digital exposure value. The imaged photosensitive medium is subsequently developed by the processor to produce a hardcopy of the image.
Digital imagers and processors of the type discussed above are well known and in widespread use. The commercially available 3M Laser Imager and Laser Imager Plus utilize silver-halide photographic film as the photosensitive media. The silver-halide film imaged by these imagers can be developed in the 3M Model XP-515 Laser Processor which makes use of conventional silver-halide photographic development techniques.
Film media used with the photographic-type digital imagers described above is coated with a silver-based emulsion. Small amounts of the emulsion are activated and converted into metallic silver when struck by the laser beam. The greater the intensity of the laser beam that strikes a pixel area on the film, the greater the density of the metallic silver formed at that location. The imaged film is developed by passing the film through tanks of developing solutions which react with the activated emulsion to form a visible deposit of metallic silver. The density or amount of metallic silver at each pixel on the developed film corresponds to the degree to which the emulsion was activated when that individual pixel was struck by the laser beam. As a result, the greater the intensity of the light that reaches a given pixel on the film, the more emulsion that is activated and the denser the silver deposit on the developed image.
Automatic film processors require replenishment of the developer chemical solutions depleted during the development of silver-halide film. The rate at which the developer solutions are depleted depends upon the density (overall lightness or darkness) of silver on the developed film, and therefore the amount of activated emulsion on the imaged but undeveloped film. Conventional automatic film processors typically include a controller actuated replenishment mechanism for replenishing the developer solutions at a predetermined rate such as a specific volume per sheet of film developed, or at some other rate determined by the experience of the operator.
Since the amount of developer solution required depends upon the overall silver content of the film, a film with a greater content of silver will require greater amounts of developer solution. For this reason, fixed developer replenishment rates may not be sufficient if a number of high silver content films are developed in sequence. The result would be poorly developed film. On the other hand, developer solution is wasted if the replenishment rate is greater than that needed to maintain the required concentration.
A method for determining the supplementary amount of developing solution for a film processor used in conjunction with a half-tone dot image generator is disclosed in the Sakamoto et al. U.S. Pat. No. 4,310,234. As described in this patent, an analog width signal controls the width of half-tone dots recorded on photographic film. The width signal is applied to a converter and converted into a frequency variation for counting by a counter. The counter counts up integrally the values of the width signals as the frequency variations from the start to the end of the scanning operation of a sheet of film. The integrated value of the width signals corresponds to the total exposure area of the photographic film and, therefore, the supplementary amount of developing system. The integrated value of the width signals is transferred to the developer and used to control the supplementation of developing solution. However, this method is not configured for continuous tone digital imagers.
It is evident that there is a need for improved developer replenishment control systems and associated media processors used in conjunction with continuous tone digital imagers. The replenishment control system and media processor must be capable of replenishing the developer solutions at a sufficient rate to accommodate peak developer needs, yet prevent waste during periods when lesser amounts of developer are required. Any such systems must also be efficient and reliable to be commercially viable.